Well, I figured they were next to free, so I'm embarking on my first porting job. I have the swirl port truck heads (don't have the number handy right now) and after reading David Vizard's book on horsepower, I took a long look at the bowls in the intake ports.
The intake port flow is biased entirely to one side. It is supposed to flow around the base of the valve guide and hit the ramp, imparting max swirl when the valve opens. Vizard's book shows some soft rubber molds he made of good ports, and they show only a slight bias on one side of the port - but he says that imparts enough swirl.
That being the case, I decided to slice off the ramp even with the top of the valve guide and do other general bowl smoothing. I also smoothed the lip under the seat.
My question is, has anyone actually ported these heads, and am I improving them or by removing the ramp am I taking out the only good part about them? Part of the ramp is still there, and the bias is pretty much cast into the head, so there should still be plenty of swirl. I just wanted to remove as much restirction as possible.
I'll be putting a 144 blower on the engine, so I'm not TOO concerned, I just wanted some general advice.
Thanks!

The ramp is there to promote swirl (rotating flow) inside the cylinder, so that when the plug ignites, the mixture burns quickly. In the mid 80s GM called it a fast burn head, and they typically needed only 24 to 30 degs of ignition advance for optimum torque and power. It was used on passenger car and light truck 4.3, 5.0 and 5.7 TBI Chevy & GM engines, on 2.5 liter 4 cyl GM engines, and v8 Olds and Cadillac 5.0 engines (307). None of these engines was ever intended for sporty use, so all used small cams and were strangled by poor flowing exhausts. They made decent torque but the engine power rating never went above 210 fwhp @ 4500 rpm (C/K/G 5.7 truck engines).

Even with that said, a cam swap and a exhaust change will bring the power level up to 250+ on a 5.7 TBI Chevy v8 even with no porting done to the heads -- proven by a Camaro owner who used a junkyard Cadillac TBI 350, added a 214 deg cam, a carburator (sidestepping the ECM retuning) and a decent exhaust. That car went 13.6 @ 101 mph in the quarter, which puts it close to a 93-97 LT1 Fcar (275 fwhp).

The ramp isn't a new idea, nor was it in the mid 80s. They had been used in diesel engines for years for the same reason. In a gas engine, it also gave better fuel economy and greater resistance to detonation so it was useful when burning lower octane fuel.

As far as removal of the ramp --- it's a lot of work and probably not a good idea. That doesn't mean you can't do some porting however, and it's been proven by many people that the gains are substantial. Go here and start reading:

Well, I figured they were next to free, so I'm embarking on my first porting job. I have the swirl port truck heads (don't have the number handy right now) ..... My question is, has anyone actually ported these heads, and am I improving them or by removing the ramp am I taking out the only good part about them? .... I'll be putting a 144 blower on the engine, so I'm not TOO concerned, I just wanted some general advice.
Thanks!

Fast355 has ported those heads (810, 191 and 193 are the last three digits of the casting number, as used on trucks and car with the 350), AND and is using them on a TBI engine with a 144 blower on it. Read the posts and write to him via PM:

THANKS!! Those posts and links truly answered my questions. I notice that some of the posts say that swirl helps cut down detonation, which is EXACTLY what is needed on a blown motor.
Low end torque with the blower and those heads should be outstanding.
As far as high end HP, I'd say that lopping off the top of the ramp and porting will help high end flow. That and using high gears on such a light car (along with a T56 5 or 6 speed tranny) should be a hoot to drive.
I think my problem is going to be traction, not torque or HP.
Thanks again.

THANKS!! Those posts and links truly answered my questions. I notice that some of the posts say that swirl helps cut down detonation, which is EXACTLY what is needed on a blown motor.

I couldn't agree more.

Quote:

Low end torque with the blower and those heads should be outstanding. As far as high end HP, I'd say that lopping off the top of the ramp and porting will help high end flow.

Funny you should mention that.

I have read in several places, but could never find the actual source, that GM considered the heads as having "too much swirl"; that they spent a lot of time/effort/money to develop them only to find out later that slightly less swirl was good enough, while allowing more airflow (and hence more power). The heads that replaced them had less swirl and much better airflow --- they were, of course, the LT1 (in both aluminum and iron) and later the Gen 1 version called the L31 and L30 Vortec heads.

So when I look at the 187 swirl port heads that I'm porting in my basement, I saw the same thing you did. There's no point is removing the ramp entirely (too much work, plus the ramp is useful from reasons that have been explained before), but when you want more airflow, the very top of the ramp can be seen to be a flow impediment especially if you look into the port (from the intake manifold side).

Removing the very top of the ramp should still maintain most of the swirl (especially at part throttle and low rpms) but provide more airflow at higher engine speeds.

Quote:

That and using high gears on such a light car (along with a T56 5 or 6 speed tranny) should be a hoot to drive. I think my problem is going to be traction, not torque or HP. Thanks again.

IIRC you are in Austin. Fast355 (aka Chris) is in DFW area. That's close enough to get a good dialogue going. HTH and keep us posted on how it goes.

EDIT: look in the link to the head flow data, and then look carefully at the pix of the 4.3 v6 head ported for the HRM article. It looks like they removed the very top part of the ramp, which is pretty much what you mentioned and what I had been thinking about. This would reduce swirl slightly but it should allow more high rpm flow.

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